/Engine/Source/Runtime/CoreUObject/Public/UObject/PackageResourceManager.h
Open a seekable binaryFArchiveto read the bytes of the given External Resource. An ExternalResource is in a separate domain from the one out of which this ResourceManager serves PackagePaths.
The openedFArchive, or nullptr if it wasn't found.
[TUniquePtr](API\Runtime\Core\Templates\TUniquePtr)< [FArchive](API\Runtime\Core\Serialization\FArchive) > OpenReadExternalResource ( EPackageExternalResource ResourceType, FStringView Identifier )